Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/20096#discussion_r160006676
--- Diff:
external/kafka-0-10-sql/src/main/scala/org/apache/spark/sql/kafka010/KafkaContinuousWriter.scala
---
@@ -0,0 +1,113 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.kafka010
+
+import org.apache.kafka.clients.producer.{Callback, ProducerRecord,
RecordMetadata}
+
+import org.apache.spark.internal.Logging
+import org.apache.spark.sql.{Row, SparkSession}
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions.{Attribute, Cast,
Literal, UnsafeProjection}
+import
org.apache.spark.sql.kafka010.KafkaSourceProvider.{kafkaParamsForProducer,
TOPIC_OPTION_KEY}
+import org.apache.spark.sql.sources.v2.streaming.writer.ContinuousWriter
+import org.apache.spark.sql.sources.v2.writer._
+import org.apache.spark.sql.streaming.OutputMode
+import org.apache.spark.sql.types.{BinaryType, StringType, StructType}
+
+/**
+ * Dummy commit message. The DataSourceV2 framework requires a commit
message implementation but we
+ * don't need to really send one.
+ */
+case object KafkaWriterCommitMessage extends WriterCommitMessage
+
+/**
+ * A [[ContinuousWriter]] for Kafka writing. Responsible for generating
the writer factory.
+ * @param topic The topic this writer is responsible for. If None, topic
will be inferred from
+ * a `topic` field in the incoming data.
+ * @param producerParams Parameters for Kafka producers in each task.
+ * @param schema The schema of the input data.
+ */
+class KafkaContinuousWriter(
+ topic: Option[String], producerParams: Map[String, String], schema:
StructType)
+ extends ContinuousWriter with SupportsWriteInternalRow {
+
+ override def createInternalRowWriterFactory():
KafkaContinuousWriterFactory =
+ KafkaContinuousWriterFactory(topic, producerParams, schema)
+
+ override def commit(epochId: Long, messages:
Array[WriterCommitMessage]): Unit = {}
+ override def abort(messages: Array[WriterCommitMessage]): Unit = {}
+}
+
+/**
+ * A [[DataWriterFactory]] for Kafka writing. Will be serialized and sent
to executors to generate
+ * the per-task data writers.
+ * @param topic The topic that should be written to. If None, topic will
be inferred from
+ * a `topic` field in the incoming data.
+ * @param producerParams Parameters for Kafka producers in each task.
+ * @param schema The schema of the input data.
+ */
+case class KafkaContinuousWriterFactory(
+ topic: Option[String], producerParams: Map[String, String], schema:
StructType)
+ extends DataWriterFactory[InternalRow] {
+
+ override def createDataWriter(partitionId: Int, attemptNumber: Int):
DataWriter[InternalRow] = {
+ new KafkaContinuousDataWriter(topic, producerParams,
schema.toAttributes)
+ }
+}
+
+/**
+ * A [[DataWriter]] for Kafka writing. One data writer will be created in
each partition to
+ * process incoming rows.
+ *
+ * @param targetTopic The topic that this data writer is targeting. If
None, topic will be inferred
+ * from a `topic` field in the incoming data.
+ * @param producerParams Parameters to use for the Kafka producer.
+ * @param inputSchema The attributes in the input data.
+ */
+class KafkaContinuousDataWriter(
+ targetTopic: Option[String], producerParams: Map[String, String],
inputSchema: Seq[Attribute])
+ extends KafkaRowWriter(inputSchema, targetTopic) with
DataWriter[InternalRow] {
+ import scala.collection.JavaConverters._
+
+ private lazy val producer = CachedKafkaProducer.getOrCreate(
+ new java.util.HashMap[String, Object](producerParams.asJava))
+
+ def write(row: InternalRow): Unit = {
+ checkForErrors()
+ sendRow(row, producer)
+ }
+
+ def commit(): WriterCommitMessage = {
+ // Send is asynchronous, but we can't commit until all rows are
actually in Kafka.
+ // This requires flushing and then checking that no callbacks produced
errors.
+ producer.flush()
--- End diff --
maybe check for errors first before doing a flush and flush can take a long
time and its better to fail earlier if possible.
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